This study evaluated the toxicity effects of chlorpyrifos on bobwhite quail (Colinus virginianus) kept in 27 field-exposed large pens arranged over turf in a randomized block design with nine blocks of three pens (16 adult birds per pen). Nine pens were treated with one application of 3.4 kg active ingredient (ai) per hectare followed by a second 3.4 -kg ai/ha application 2 weeks later, nine pens with one 6.7 -kg ai/ha application, and nine pens with formulation blank. In addition, the seed fed to the birds in the two chemically treated pens was also treated with chlorpyrifos. Mean residue in the grass samples from the first 3.4-kg treatment pens ranged from 306+/-95 ppm on day 0 to 18+/-8 ppm on day 14 after treatment. The second 3.4 -kg ai/ha treatment grass residues ranged from 361+/-167 ppm on day 0 to 38+/-24 ppm on day 14 after treatment. Grass residues from the 6.7-kg treatment pens ranged from 903+/-310 ppm on day 0 to 9+/-8 ppm on day 30 after treatment. Half-lives were approximately 2 days and 10 days for grass and seeds, respectively. Whereas the incidence of behavioral deficits was significantly (P = 0.0156) higher in the 6.7-kg pens (five females, one male), two of the females could have been the same bird because they were both seen in the same pen on days 23 and 24 after treatment. There was no significant difference in mortality, brain acetylcholinesterase activity, or any other measured parameter among any of the treatments. We conclude that application of chlorpyrifos to turf at 3.4 and 6.7 kg ai/ha is not expected to have chronic deleterious effects on populations of bobwhite quail grazing on treated grass or seeds, provided there is an abundant supply of seeds for the quail to eat.